Fixed typos about vncunused in xmexamples

diff -r cc953475ab14 tools/examples/xmexample1
@@ -90,7 +90,7 @@ disk = [ 'phy:hda1,hda1,w' ]
 #
 # Or you can bind the first unused port above 5900:
 #
-# vfb = [ 'type=vnc,vnclisten=0.0.0.0,vnunused=1' ]
+# vfb = [ 'type=vnc,vnclisten=0.0.0.0,vncunused=1' ]
 #
 # You can override the password:
 #

diff -r cc953475ab14 tools/examples/xmexample2
@@ -126,7 +126,7 @@ disk = [ 'phy:sda%d,sda1,w' % (7+vmid),
 #
 # Or you can bind the first unused port above 5900:
 #
-# vfb = [ 'type=vnc,vnclisten=0.0.0.0,vnunused=1' ]
+# vfb = [ 'type=vnc,vnclisten=0.0.0.0,vncunused=1' ]
 #
 # You can override the password:
 #

diff -r cc953475ab14 tools/examples/xmexample3
@@ -111,7 +111,7 @@ disk = [ 'phy:hda%d,hda1,w' % (vmid)]
 #
 # Or you can bind the first unused port above 5900:
 #
-# vfb = [ 'type=vnc,vnclisten=0.0.0.0,vnunused=1' ]
+# vfb = [ 'type=vnc,vnclisten=0.0.0.0,vncunused=1' ]
 #
 # You can override the password:
 #